Electrolytic capacitor

ABSTRACT

The present invention relates to a safety vented structure of an electrolytic capacitor containing a capacitor element (1) in a case (2), wherein a safety vent (7) is constituted by providing on a bottom face of the case (2) a first narrow groove (7a) which passes through the center (P) of the bottom of the case (2) and a second narrow groove (7b) which crosses with right angle the first narrow groove (7a) at a crossing point (Q) outside a winding center part (5) of the capacitor element (1) and is longer than the first narrow groove (7a); thereby short-circuiting which arises at the time of operation of the safety vent is prevented.

TECHNICAL FIELD

The present invention relates to an electrolytic capacitor whereincapacitor element is enclosed in a case made of metal.

BACKGROUND ART

Hitherto, in the capacitor of this kind a safety vented structure isnecessary, since when an excessively large current flows as a result ofa circuit trouble the capacitor element is liable to be heated and alarge amount of gas is produced, thereby to increase pressure in thecase to generalte a danger of explosion.

As the safety vented structure, generally is adopted such a measure thata safety vent of decreased thickness is provided on sealing member of asealed case or the case as such, so that, when gas pressure in the casereaches a value immediately before explosion, the safety vent isoperated by the gas pressure to discharge the gas, thereby to preventthe explosion before its happening.

FIG. 1 shows representative structure of the sealed type electrolyticcapacitor. In the figure, numeral 1 designates a capacitor elementsoaked with electrolyte, numeral 2 designates a cylindrical case made ofmetal for enclosing the capacitor element 1, numeral 3 designates asealing member for sealing an opening part of the case 2, numeral 4designates terminals fixed to the sealing member 3. The capacitorelement 1 is constituted by winding anode foil having anodic oxide filmand a cathode foil with electrolytic paper inbetween, and a partdesignated by dotted lines is winding center part. A safety vent 6 ofdecreased thickness is provided at the bottom part of the case 2.

As to this safety vent, hitherto various kinds are invented or devisedand reduced into practice. FIG. 2A through 2C show one example thereof,and FIG. 2A is a case which provides +* shaped safety groove 6a whichcrosses at center P of a bottom face of a case 2, FIG. 2B is a casewhich provides safety groove 6b of V letter shape, and FIG. 2C is a casewhich provides a ring-shaped safety groove 6c.

Hereupon, when an excessively large current flows as a result of circuittrouble, the capacitor element 1 generates heat, and specially thetemperature at the winding center part 5 becomes 10°-20° C. higher thanperipheral part. Accordingly, when the safety vent 6 provided at thebottom of the case operates, gas generated in the case is dischargedpassing almost through the winding center part 5. Since this windingcenter part 5 has unstable beginning end from which electrode foil andelectrolytic paper constituting the capacitor element are started to bewound, it is liable to be deformed, and by gas discharging at operationof the safety vent 6 the winding center part 5 is deformed to be pulledoutside. Accordingly, when the safety groove 6a, 6b and 6c operate thecapacitor element 1, a part of the winding center part 5 is pulled outas shown in FIGS. 3A, 3B and 3C, thereby to make short-circuiting ofanode and cathode of the capacitor element 1, and such a short-circuitaccident is generated that a circuit using the electrolytic capacitor isshort-circuited thereby to destroy other components, too.

DISCLOSURE OF THE INVENTION

Therefore, the present invention intends to provide electrolyticcapacitors wherein in an electrolytic capacitor containing a capacitorelement in a case, wherein a safety vent is constituted by providing ona bottom face of the case a first narrow groove which passes through thecenter of the bottom of the case and a second narrow groove, whichcrosses with right angle the first narrow groove at a crossing pointoutside a winding center part of the capacitor element and is longerthan the first narrow groove, and thereby even when the safety ventoperates the winding center part 5 is not pulled outside, andaccordingly, no short-circuit accident arises.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is the lengthwise cross-sectional view of the generalelectrolytic capacitor, FIGS. 2A through 2C are the plan views showingthe safety vent of the conventional electrolytic capacitor, FIGS. 3Athrough 3C are lengthwise cross-sectional views showing the states ofthe electrolytic capacitors when the coventional safety vent works, FIG.4 is a plan view showing a safety vent of an electrolytic capacitor inaccordance with one embodiment of the present invention, FIG. 5 is alengthwise cross-sectional view of the same, FIG. 6 and FIG. 7 are planviews showing other examples of safety vent of electrolytic capacitorsof the present invention, respectively, FIG. 8 is a lengthwisecross-sectional view showing a state when a safety vent of anelectrolytic capacitor of the present invention.

THE BEST MODE FOR EMBODYING THE INVENTION

FIG. 4 and FIG. 5 show one embodiment of safety vented case ofelectrolytic capacitor in accordance with the present invention, and inFIG. 4 numeral 7a is linear first narrow groove which passes through thecenter P of a bottom face of the case 2, numeral 7b is a second narrowgroove which crosses the first narrow groove 7a at a cross point Q otherthan the point P and is equally divided into two parts, and a safetyvent 7 is consisted of the first and second narrow grooves 7a, 7b. And,the cross point Q of the first and second narrow grooves 7a, 7b isoutside a winding center part 5 of a capacitor element 1. And the secondnarrow groove 7b is equally divided into two parts at the cross point Q,and the overall length b thereof is designed to be longer than thelength a of the first narrow groove 7a.

Incidentally, the first narrow groove 7a and the second narrow groove 7bmay be provided on either of the inside or outside of the bottom face ofthe case 2, and as shown in FIG. 6, the second narrow groove 7b may beprovided in two lines with respect to the center P as point of symmetry;and furthermore, as shown in FIG. 7 similar effect is obtainable evenwhen the second narrow groove 7b is provided to cross from one end tothe other end of the bottom face of the case 2.

By such configuration, the following effects of operation areobtainable:

(1) a position where the safety vent operates by the gas pressure in thecase is along the second narrow groove 7b rather than the cross point Q,and is situated outside of the winding center part 5, and accordinglyeven when the gas blows out the winding center part 5 of the capacitorelement 1 is not pulled out outside, and

(2) since the configuration of the safety vent is of left-rightsymmetry, the pressure effectively operates, and reliability of theoperation of the safety vent is high, and operation sound of the safetyvent is very small.

In order to confirm function and effect of the present invention,experiments are carried out based on the below-mentioned samples. Thetest method is AC voltage method of EIAJ, RC-3807.

Incidentally, among the below-mentioned Table 1 and Table 3, as shown byFIG. 4 and FIG. 5, "a" is length of the first narrow groove 7a, "b" islength of the second narrow groove 7b, "c" is length between P-Q, "d" isthickness of the narrow grooves, "e" is thickness of bottom face of thecase 2, and "F" is operation pressure of the safety vent.

Table 2 is test results of safety vent operation states by theconventional safety vents A, B and C, respectively of FIGS. 2A through2C.

And, Table 1 and Table 2 are those using as samples the electrolyticcapacitors which is of ratings of 200 V, 470 μF, using aluminum case of30 mm Φ×40 mm as its case, and winding center part of the capacitorelement being 6 mm Φ, and numerals of the tables are average value oftwenty samples. Table 3 is those using as samples the electrolyticcapacitors which is of ratings of 16 V, 2200 μF, using aluminum case of16 mm Φ×25 mm as its case, and winding center part of the capacitorelement being 2 mm Φ, and numerals of the table is average value oftwenty samples.

                  TABLE 1                                                         ______________________________________                                                                                     Rate of                                                                       short-                           No.  a[mm]   b[mm]   c[mm] d[μ]                                                                            e[μ]                                                                            F[Kg/cm.sup.2 ]                                                                       circuit                          ______________________________________                                        1    19      20      5     110  650  10.5      0%                             2    19      18      5     110  650  11.5    20                               3    17      19      5     110  650  11.5     0                               4    17      15      5     110  650  12.0    25                               5    15      17      5     110  650  12.0     0                               6    15      13      5     110  650  13.0    30                               ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                                                Rate of                                                                       short-                                No.   Prior art  d[μ] e[μ]                                                                             F[Kg/cm.sup.2 ]                                                                        circuit                               ______________________________________                                        7     Conventional                                                                             110     650   11.0      50%                                        safety vent A                                                           8     Conventional                                                                             110     650   11.5     80                                          safety vent B                                                           9     Conventional                                                                             110     650   12.5     90                                          safety vent C                                                           ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                                                                     Rate of                                                                       short-                           No.  a[mm]   b[mm]   c[mm] d[μ]                                                                            e[μ]                                                                            F[Kg/cm.sup.2 ]                                                                       circuit                          ______________________________________                                        10   11      12      2     95   450  20        0%                             11   11      10      2     95   450  22      30                               ______________________________________                                    

As the numerals of the above-mentioned Table 1, Table 2 and Table 3show, in those with the conventional safety vents, the rates ofshort-circuit are generating at a very high probabilities as 50-90%,while No. 1, No. 3, No. 5 and No. 10 of a <b has no short-circuits atall even at safety vent operation. On the other hand, No. 2, No. 4, No.6 and No. 11 of a >b make short-circuits, 20-30% being pulled out ofeach one part of the winding center part 5 of the capacitor element 1.

That is, in No. 1, No. 3, No. 5 and No. 10 of a <b, their second narrowgrooves 7b are largely cut and capacitor element 1 at the operation ofthe safety vent becomes as shown by FIG. 8, and winding center part 5 isnot positioned at the operation position of the safety vent, andaccordingly the winding center part 5 of the capacitor element 1 is notpulled outside and no short-circuit is produced. However, in the casesof No. 2, No. 4, No. 6 and No. 11 of a >b, the first narrow groove 7a iscut from the cross point Q, and hence operation position of the safetyvent nears to the winding center part 5, and accordingly the windingcenter part of the capacitor element 1 is liable to be pulled out, andrate of generation of the short-circuit becomes high.

As has been described, in the present invention the defects which theconventional safety vents of FIG. 2 and FIG. 3 have had are dissolved,and it is experimentally confirmed that the purpose of the invention isachieved.

Incidentally, although in the safety vent of the present invention theoperation effect of the safety vent is the same even when the decreasedthickness parts are provided on the inside part or outsidepart of thebottom face of the case, in case the decreased thickness part is onoutside there is a liability that a protrusion or the like directlystrikes the decreased thickness part, thereby to damage the decreasedthickness part; and therefore it is dedirable that the decreasedthickness part is on the inside as shown by FIG. 5.

And it is necessary that the second narrow groove 7b should be longerthan the first narrow groove 7a, and difference between the length isdesirably more than 1 mm when considering working accuracy in case ofproviding the narrow grooves.

POSSIBLE UTILIZATION IN INDUSTRY

As has been described in the above, according to the electrolyticcapacitor of the present invention, by making safety vent by providingon a bottom face of a case, a first narrow groove which passes throughthe center of the bottom of the case and a second narrow groove whichcrosses with right angle the first narrow groove at crossing pointoutside a winding center part of the capacitor element, and is longerthan the first narrow groove; and thereby, operation position of thesafety vent is not at a position of the winding center part which islargest of deformation against deformation of the capacitor element atthe time of operation of the safety vent, and accordingly generation ofshort-circuit trouble by pulling outside of the winding center part isprevented; and thereby even when the electrolytic capacitor isdestroyed, there is no generation of damaging other components.

We claim:
 1. An electrolytic capacitor containing a capacitor element ina case, wherein a safety vent is constituted by providing on a bottomface of said case a first narrow straight groove which passes throughthe center of said bottom face of said case and a second said firstnarrow groove between the ends thereof at a crossing point outside awinding center part of said capacitor element and is longer than saidfirst narrow groove.
 2. An electrolytic capacitor in accordance withclaim 1, wherein said second groove is provided in a manner to beequally divided into two parts at said crossing point with said firstnarrow groove.
 3. An electrolytic capacitor in accordance with claim 1,wherein said first narrow groove and said seoond narrow groove areprovided by forming decreased thickness parts, inside of said bottomface.
 4. An electrolytic capacitor in accordance with claim 1, whereindifference of lengths of said first narrow groove and said second narrowgroove is made above 1 mm.